METAZOA CRUSTACEA. 337 



region. Six of these are similar, while the seventh or 

 terminal segment is larger, rounder, and flattened on the 

 edges. The five anterior abdominal segments carry five 

 pairs of similar jointed swimming-feet, while the sixth 

 bears a pair of modified swimming-feet. The slight varia- 

 tion in the structure of all the swimming-feet excepting 

 the last two indicates that they perform a similar function. 

 Each swimming-foot is made of two leaf-like parts 

 fastened to a stem ; the former are fringed with long 

 hairs. Attached to the base of each swimming-foot is a 

 gill made up of filaments. The last pair of swimming- 

 feet are longer and stronger than the others. They con- 

 sist of more sections and joints, and the basal section 

 does not bear a gill. These two swimming-feet with the 

 large terminal segment, which is without appendages, 

 constitute an efficient organ for propelling the animal 

 through the water. 



In front of the abdomen are four similar segments 

 which are much smaller and narrower than the abdominal 

 segments already described. Three of these segments 

 bear slender little organs resembling walking-legs, while 

 the remaining segment bears a pair of appendages very 

 different from the walking-legs, but similar to the two 

 pairs of appendages in front of them. The segments 

 bearing the mouth parts and one pair of antennae are 

 consolidated and covered in part by the carapace, so 

 that the number can only be inferred by the number of 

 appendages. 



In front of the walking-feet are three pairs of organs 

 that are alike in shape and which terminate in a curved 

 movable jaw. Then come the large grasping organs and 

 in front of them a slender pair of appendages. These 

 five pairs are the maxillipeds. In front of the maxillipeds 

 are three pairs of small maxillae and one pair of short 

 antennae. 



The first two segments of the body bearing the eye- 

 stalks and first pair of antennae are freely movable, and 

 in this respect Squilla differs from other Crustacea. 



